The research proposed is designed to identify and characterize metabolic benefits of an amino acid formula enriched with branched chain amino acids (BCAA) compared with a balanced amino acid mixture in the nutritional support of injury metabolism. The paired studies described would utilize a controlled, reproducible human model of injury metabolism. Specifically they would: 1. determine the relative efficiency of BCAA enriched and balanced amino acid mixtures in achieving nitrogen equilibrium during induced injury metabolism; 2. characterize the metabolic alterations induced in this model when nitrogen equilibrium was maintained both with BCAA enriched and balanced amino acid mixtures; 3. determine differences in those responses noted above (#2) that could be attributed to the composition of the nitrogen source.